Many kinds of sheet-like foods made from proteins have been known. They can be classified into non-swollen film type foods such as "yuba (membrane-like Japanese traditional soybean protein food)" and edible films and swollen type foods such as "aburaage (fried soybean curd)".
As for methods of swelling, frying (heating in oil) and microwave heating are known.
Frying is a method wherein heat conducts from the outside to the inside of food materials by heating outside. In fried food materials, not only the oil oozes out of the materials, but also the fried products have cavities therein and swollen appearances.
Microwave heating is a method which heats the inside of materials by an electromagnetic wave. Comparing with frying which heats the outside of the materials, microwave heating is better in that quick inside heating can be obtained. Following microwave heating methods, most of which are used as means for drying, have been known.
For example, JP-B 60-38100 discloses a process for preparing foods having yuba-like structure, which are swollen spongy form by high-frequency heating to form spongy materials. However, there is no disclosure of intermittent irradiation.
JP-A 61-128842 discloses sheet-like foods and microwave heating for heat coagulation drying. However, there is no disclosure of intermittent irradiation.
JP-A 2-171155 discloses a process for preparing membrane-like foods. However, microwave heating is used only for heat-drying and there is no disclosure of intermittent irradiation.